Difference between clean, gradlew clean

What is the difference between the following statements when issued from a Android Studio Project's terminal :

Android_Studio_Project_Path: ./gradlew clean

Android_Studio_Project_Path: ./gradlew clean assembleDebug

Android_Studio_Project_Path: ./gradlew clean :assembleDebug

and normal Android Studio --> Build --> Clean.

What would be the difference in the internal process.

1. ./gradlew clean

   Uses your project's gradle wrapper to execute your project's clean task. Usually, this just means the deletion of the build directory.

2. ./gradlew clean assembleDebug

   Again, uses your project's gradle wrapper to execute the clean and assembleDebug tasks, respectively. So, it will clean first, then execute assembleDebug, after any non-up-to-date dependent tasks.

3. ./gradlew clean :assembleDebug

   Is essentially the same as #2. The colon represents the task path. Task paths are essential in gradle multi-project's, not so much in this context. It means run the root project's assembleDebug task. Here, the root project is the only project.

4. Android Studio --> Build --> Clean

   Is essentially the same as ./gradlew clean. See here.

For more info, I suggest taking the time to read through the Android docs, especially this one.